Audio amplifier response control



July 27, 1943. w HEPPV AUDIO AMPLIFIER RESPONSE CONTROL Filed June 14, 1941 INVENTOR erner Hep .7 BY Z Am/W n'omusv Patented July 27, 1943 ;UNITED S ES PATENT- OFFICE AUDIO AME'LIFIER RESPONSE CONTROL Werner HepmBerlin, Germany; vested in the I Alien Property Custodian Application June 14, 1941, Serial No. 398,085 In Germany January 26, 1940 9 clams; (01. 250-2 frequencies so that, in a positively acting mannor, the higher audio frequencies are suppressed more markedly than in local reception as a result of higher amplification, or gain, of the con trolled audio tube in distant signal reception.

' Now, according to this invention a particularly effective regulation is secured by feeding the audio potential to the control grid of a tube serving to amplify a regulation potential, especially the amplifier system of a tuning indicator tube, and. by derivingthe said potential from the plate circuit of the regulator potential amplifier tube and using it for negative feedback. In this manner, on the one hand, the influence of the regulator potential on the band width is made more intense, while, on the other hand, there result particularly high maximum negative feedback potentials.

In the appended drawing, showingsuch a circuit scheme by way of example, there is shown a double diode tube V1 and the regulated audio tube V2. The latter is controlled by means of the regulatorpotentialobtained in the righthand diode. The tuning indicator tube is V3, and the screen grid type of power tube is V4. The indicator tube V3 is fed through the resistances R2,. R3 withv an AVC. potential taken off across R1, and the potential is smoothed by condenserCs so as to act as an indicator control quantity. The tube V3 may be of the 6E5 typ The voltage across R1 isproportional to the carrier amplitude. R1 is a high-ohm resistance included in the screen gridcircuit of the power tube V4 across which an audio alternating pot'ential arises. This alternating potential is ap-. V

plied through condenser C1 to the regulator grid feed-back will be operative predominantly for the highest audio frequencies, particularly in the range of 9 kilocycles (kc). So far as the other circuit elements are concerned, the problem of constants is immaterial and they have no new significance. Hence, these elements in so far as they appear in the drawing are devoid of no tations or symbols.

The negative feedback potential is intentionally taken from the screen grid circuit of tube V4 rather than from the plate circuit. For it will be understood that the plate circuit contains v a 9 kc. trap,'or stopper circuit, Sp which, if the; negative feedback potential were derived from the plate, would have the effect that, for these. frequencies, also'the negative, feedback potentialis of a minimum value, not to'mention this further difficulty that, if the said potential were; taken from theplate circuit, undesirable phase;

.tive feedback potential from the plate of thepre-- ceding tube V2, if V3 is employed at the same time, is impracticable on the ground that this.

would mean the production of regeneration ratherthan negative feedback. In other words, it is not merely for the sake of amplification, but also to insure the properphase angle, that tube V; is also included in the scheme.

In lieu of the resistance R7 shown in the drawing, it is possible also to use a resistance with frequency effect, more particularly a choke-coil or a resonance circuit tuned to the high frequencies. In fact, this offers an advantage, first, because this restricts the negative or reverse feedback still more to the high frequencies. In other words, the slope of the band width curve is made steeper. In the second place, an appre ciable' frequency-dependent resistance in the screen grid lead inheres action on the amplification'factor of the tube under conditions being a, function of the frequency seeing that such screen grid alternating potentials as will arise produce a negative feedback effect. In other words, the frequencies used for the reverse feed- 7 back are taken from the end or power tube in such a way that the'gain of the power tube for thesefrequencies is atfltheisa'metime reduced. It will thus be seen that a circuit "element which is a function of the frequency instead of resistance R1 results in a multiplicative action upon the frequency characteristic or response. However, the use of this effect is of practical sense only if a parallel resonance circuit tuned to 9 kc,

is included in the screen grid lead, since the9 kc. stopper circuit may be operative both for long distance as well as in local signal reception, whereas general suppression of the high frequencies by direct screen grid reverse feedback is not desirable; for this is not subject to automatic volume control action and is therefore constantly operable. If the resonance circuit connected in lieu. of resistahceEv should happen to exhibit a tendency towards phase shift, this would have to be offset by a counteracting phase shift in the next reverse feedback I path.

What is claimed is:

1. In aradio receiver of the type providedwith a source of audio-modulated carrier waves, a detector for producing audio voltage from the waves, an audio amplifier for the audio voltage,

and a visual current indicator tube the improvement which comprises means for impressing amplified audio voltage upon said indicator tube, means impressingthe audio Voltage output of the indicator tube upon the inputoi said amplifierin degenerative sense, and means responsive to carrier amplitude variation for varying the gain of the indicator tube.

2. In the receiver of the type providcdwith a demodulator of sound modulated carrier waves, an audio amplifier network having input terminals coupled to said demodulator, a tuning in-, dicator tube of, the type-having a control electrode, an output electrode and a fluorcescent target; the improvement which comprises means responsive to the amplified audio output of said audio amplifier for varying said indicator tube amplified audio output of said audio amplifier for varying said indicator tube control electrode potential, and means for feeding amplified audio potential developedat the output electrode of said indicator tube to, the input terminals of the audio amplifier. l f

4. In an audio amplifier system comprising at least two audio amplifier tubes arranged in cascade; the last tube including a positive output, element and an auxiliary control element, a resistive element in circuit with the auxiliary element for developing amplified audio voltage thereacross, audioutilizing means in circuit with the output element or" the last tube, means including an amplifier tube to feed' the audio voltage developed across said resistive element. to the input electrode of the first audictube in degenerative phase, and automatic volume control means to vary the control electrode voltage of said amplifier tube. 5;;[11 the radioreceiver of the typeprovided with a demodulator of sound modulated carrier waves, an audio amplifier network having input terminals coupled to said demodulator, a tuning indicator tube of the type having a control electrode, an output electrode and a linerescent target; the improvement which comprises means responsive to the amplified audio output of said audio amplifier for controlling saidindicator. tube control electrode potential, automatic volurne' control means-to vary the said control electrode voltage, and means for degeneratively feeding amplified audio potential developed in the output electrode circuit of said indicator tube to the input terminals of the audio amplifier:

V 6'.- In the receiver of the'type provided with a demodulator, of sound modulated carrier waves, an audio amplifier network having input terminals coupled to said demodulator, a tuning indicator tube of the type having a control electrode, an output electrode and a fluorescent target; the improvement which comprises means responsive to the amplified 'audiov output of said audio amplifier for controlling said indicator tube control electrod potential, means for degeneratively feeding amplified audio potential developed in the output'electrode circuit of said indicator tube to the input terminals of the audio amplifier, and carrier-responsive means for regulating the intensityof the degenerative potential.

'7. In an audio amplifier system comprising at least two audio amplifier tubes arranged in cascade, the last tube including a positive screen grid element, an impedance in circuit with the screen grid element, for developing. amplified audio voltage thereacross, means in circuit with the output electrode of the last tube tuned. substantially to nine kilocycles, means to feed the audio voltage developed across said impedance to the input electrode of the first audio tube in degenerative phase, and means for controlling thermagnitude of the degenerative voltage inia sense to minimize response at frequencies above said nine kilocycles.

8. In the receiver of the type provided With a demodulator of sound modulated carrier waves, an audio amplifier network having input terminals coupled to said demodulator, a second audio tube provided with a screenv circuit, a tuning indicator tube of the type having a, control electrode, an output electrode and a fluorescent target; the improvement which comprises means, responsive to the amplified audio output developed across the screen circuitor" said'second audio tube for controlling saidin'dicator tube control electrode potential, means for degeneratively feeding amplified audio potential developed in the output electrode circuit of said indicator tube to the input terminals of the audio amplifier, and means responsive to said carrier Waves for controlling themagnitudeof said degenerative potential.

9; An audio amplifier system as described in claim/i wherein said'audio utilizingmeans includes a nine kilocycle trap and wherein said resistive element is tuned to substantiallynine kilocycles. WERNER I-IEPP. 

